Peroxidases are involved in many plant processes including plant defense responses to biotic and abiotic stresses. We isolated a novel peroxidase gene CanPOD from leaves of pepper cultivar A3. The full-length gene has a 1353-bp cDNA sequence and contains an open reading frame (ORF) of 975-bp, which encodes a putative polypeptide of 324 amino acids with a theoretical protein size of 34.93 kDa. CanPOD showed diverse expression levels in different tissues of pepper plants. To evaluate the role of CanPOD in plant stress responses, the expression patterns of CanPOD were examined using Real-Time RT-PCR. The results indicated that CanPOD was significantly induced by Phytophtora capsici. Moreover, CanPOD was also up-regulated in leaves after salt and drought stress treatments. In addition, CanPOD expression was strongly induced by signaling hormones salicylic acid (SA). In contrast, CanPOD was not highly expressed after treatment with cold. Meanwhile, in order to further assess the role of gene CanPOD in defense response to P. capsici attack, we performed a loss-of-function experiment using the virus-induced gene silencing (VIGS) technique in pepper plants. In comparison to the control plant, the expression levels of CanPOD were obviously decreased in CanPOD-silenced pepper plants. Furthermore, we analyzed the effect of P. capsici on detached-leaves and found that the CanPOD-silenced plant leaves were highly susceptible to P. capsici infection. Taken together, our results suggested that CanPOD is involved in defense responses to P. capsici infection as well as abiotic stresses in pepper plants.

The most significant threat to pepper production worldwide is the Phytophthora blight, which is caused by the oomycete pathogen, Phytophthora capsici Leonian. In an effort to help control this disease, we isolated and characterized a P. capsici resistance gene, CaRGA2, from a high resistant pepper (C. annuum CM334) and analyzed its function by the method of real-time PCR and virus-induced gene silencing (VIGS). The CaRGA2 has a full-length cDNA of 3,018 bp with 2,874 bp open reading frame (ORF) and encodes a 957-aa protein. The protein has a predicted molecular weight of 108.6 kDa, and the isoelectric point is 8.106. Quantitative real-time PCR indicated that CaRGA2 expression was rapidly induced by P. capsici. The gene expression pattern was different between the resistant and susceptible cultivars. CaRGA2 was quickly expressed in the resistant cultivar, CM334, and reached to a peak at 24 h after inoculation with P. capsici, five-fold higher than that of susceptible cultivar. Our results suggest that CaRGA2 has a distinct pattern of expression and plays a critical role in P. capsici stress tolerance. When the CaRGA2 gene was silenced via VIGS, the resistance level was clearly suppressed, an observation that was supported by semi-quantitative RT-PCR and detached leave inoculation. VIGS analysis revealed their importance in the surveillance to P. capsici in pepper. Our results support the idea that the CaRGA2 gene may show their response in resistance against P. capsici. These analyses will aid in an effort towards breeding for broad and durable resistance in economically important pepper cultivars.

As a fruit and vegetable crop, the ornamental pepper is not just highly ornamental but also rich in nutritional value. The quality of ornamental pepper fruits is given in their contents of capsaicin, vitamin C (VC), flavonoids and total phenols. The study concentrated on the accumulation of capsaicin and dihydrocapsaicin in different tissues of 18 peppers during fruit growth and development. The results showed that the pericarp and placenta contained significantly higher levels of capsaicin than dihydrocapsaicin. Additionally, the placenta contained significantly higher levels of both capsaicin and dihydrocapsaicin compared to the pericarp. The content of capsaicin was in the range of 0–6.7915 mg·g⁻¹, the range of dihydrocapsaicin content was 0–5.329 mg·g⁻¹. Interestingly, we found that the pericarp is rich in VC (5.4506 mg·g⁻¹) and the placenta is high in flavonoids (4.8203 mg·g⁻¹) and total phenols (119.63 mg·g⁻¹). The capsaicin is the most important component using the correlation analysis and principal component analysis. The qPCR results substantiated that the expression of genes in the placenta was significantly higher than that in the pericarp and that the expression of genes in green ripening stage was higher than that in red ripening stage. This study could be utilized to select the best ripening stages and tissues to harvest peppers according to the use of the pepper and to the needs of producers. It not only provides a reference for quality improvement and processing for consumers and market but also provides a theoretical basis for high-quality pepper breeding.

Dihydroflavonol-4 reductase (DFR) is a key enzyme in plant anthocyanin synthesis and can affect the synthesis of anthocyanin. In order to explore the role of DFR in anthocyanin synthesis of capsicum, the sequence of the DFR gene family was downloaded from the Arabidopsis genome database. The study showed the presence of nine members of the DFR gene family in pepper, which are primarily localized in the cytoplasm and chloroplasts. The majority of these proteins exhibit hydrophilic characteristics, with their secondary structure predominantly consisting of α-helices and random coils. Furthermore, these genes can be categorized into four distinct subfamilies, with the gene structure and conserved motifs of CaDFR members within the same subfamily providing robust support for this classification. The promoter regions of CaDFRs are enriched with numerous light-responsive elements, phytohormone-responsive elements, stress-responsive elements, and elements associated with plant growth and development, in addition to binding sites for 35 different transcription factors. According to the results of qRT-PCR analysis, the expression level of CaDFR5 was consistent with the change of anthocyanin content, and the full length of the CaDFR5 gene was further cloned. This study provides an important reference for improving fruit colour and lays a foundation for further exploring the function of the DFR gene family.